Industrial control systems are for instance applied in manufacturing and process industries, such as chemical plants, oil production plants, refineries, pulp and paper mills, steel mills and automated factories. Industrial control systems are also widely used within the power industry. Such industrial control systems may need to comprise or be combined with devices which add safety features. Example of processes which require additional safety features other than what a standard industrial control system provides are processes at offshore production platforms, certain process sections at nuclear power plants and hazardous areas at chemical plants. Safety features may be used in conjunction with safety shutdown, fire and/or alarm systems as well as for fire-and-gas detection.
The use of advanced computer systems in safety-related control systems raises challenges in the verification of correctness of large amount of software code and the complex electronics. There exists prior art, for instance described as standards, for how a higher safety level can be obtained for such systems. Such prior art is commonly focused on the process of the development of products, both the hardware part and the software parts. It also describes diagnostic functionalities and algorithms. Prior art also addresses the higher safety level obtained in executing control systems with different hardware redundancy and software diversity. The implementation of an advanced safety-control system is normally based on a dual or triple system with some type of voting before enabling an output signal. Some safety-control systems have implemented a sufficiently safe single unit solution by focusing on design of the system and highest possible quality in implementing such systems. Both multiple unit systems and single unit systems have today often included some number of diagnostic algorithms both in software and in hardware.
An example of an industrial control system, which includes a safety-critical function, is described in DE19857683 “Safety critical function monitoring of control systems for process control applications has separate unit”. The system has a main controller bus coupled to different processors via a number of decentralized data receivers.
One example of a device in an industrial control system which has increased capability of fault detection is described in GB2277814, which concerns a fault tolerant PLC (Programmable Logic Controller) including a Central Programmable Unit (CPU). A pair of first I/O modules are connected between a positive power bus and a load. A pair of second I/O modules are connected between the negative power bus and the load. GB 2 277 814 further describes that power to the load is not disconnected upon failure of one of the I/O modules on either side of the load.
U.S. Pat. No. 6,201,997 describes a two-processor solution where both processors receive the same input data and process the same program.